It is known to use overbased detergents in an oil of lubricating viscosity to improve cleanliness. Overbased detergents include sulphonates, phenates, saligenins, salixarates or salicylates, and they provide alkalinity, typically, to neutralize sulphur-containing acids produced from the combustion of carbonaceous fuels. These detergents are prepared by a number of low and high temperature processes. However, the preparation of a highly overbased detergent is difficult e.g. the maximum TBN for sulphonate detergents is typically 400 TBN whilst other overbased detergents have even lower maximum TBN's. Further the processes for making overbased detergents require complex processing to obtain a high TBN and/or to produce a filterable overbased detergent. Therefore it would be advantageous to have a method of preparing a neutral and/or an overbased detergent with improved production processes (such as, lower in-line processing viscosity) and/or ability to make highly overbased detergents.
GB 1,096,008 discloses a lubricating composition containing dispersed alkaline earth metal compounds prepared by milling. The alkaline earth metal compounds are oil-insoluble with a particle size of 1 to 30 micrometers and are dispersed from 20 to 80 weight percent of the lubricating composition. The alkaline earth metal compounds prepared by milling are used to provide a lubricant with a direct source of TBN.
U.S. Patent Application 60/718,697 discloses a method of lubricating an internal combustion engine by supplying to the engine a metal base dispersed in an organic medium. The metal base has a high solids content and a mean particle size of at least 10 nanometers to less than 1 μm. The metal base provides the lubricant with a direct source of TBN.
U.S. Pat. No. 3,525,599 discloses a composition of matter of a dispersion of barium carbonate in an amine salt of an organic acid. The composition is prepared by carbonating barium carbonate in an amine salt of an organic acid in the presence of alcohol and a non-volatile diluent oil. The composition contains 45.8% of barium carbonate.